CAMBRIDGE (CBS) – Moderna says a third booster dose of its COVID-19 vaccine will likely be necessary this fall because of the rapid spread of the Delta variant of the coronavirus.

“We believe that increased force of infection resulting from Delta, non-pharmaceutical intervention (NPI) fatigue, and seasonal effects (moving indoors) will lead to an increase of breakthrough infections in vaccinated individuals,” the Cambridge-based company said in a presentation on earnings released Thursday.

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In a separate announcement Thursday, Moderna said its vaccine is 93-percent effective against the coronavirus six months after people get the second dose.

But in the earnings presentation, the company said it expects “neutralizing titers will continue to wane and eventually impact vaccine efficacy.”

“Given this intersection, we believe dose 3 booster will likely be necessary prior to the winter season.”

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Later in the presentation, it was noted that, “We believe a booster (dose 3) is likely to be necessary this fall, particularly in the face of Delta.”

The booster test doses are 50-micrograms, which is half of Moderna’s 100-microgram standard shot.

Moderna said the clinical data “appears to support” the 50 mcg dose, but they will wait for more data in the “coming weeks” to confirm it.

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The company is also working on a vaccine that would combine a “COVID-19 variant booster + seasonal flu booster + RSV booster,” all in a single dose.